The present invention relates to storage batteries and more specifically to lead-acid type batteries incorporating small amounts of manganese or chromium* to increase cycle life, hardness, and resistance to shedding of the positive plate. FNT * The terms "manganese" and "chromium" are used to designate any and all of the soluble species thereof that may result when a soluble salt containing manganese or chromium atoms, respectively, is introduced into the electrolyte. Such species may be any simple or complex ions of manganese or chromium, respectively.
The positive plates of secondary batteries usually are formed by one of two general methods, the Plante process and the pasted plate process. The Plante process involves charging and discharging lead electrodes in an electrolytic solution, usually consisting of dilute sulfuric acid, until anodes of lead dioxide (or peroxide) and cathodes of sponge lead are formed. Oftentimes, an oxidizing agent is included within the forming electrolyte to hasten the positive plate formation by attacking the lead and forming lead sulfate which is subsequently converted to the desired lead dioxide.
The pasted plate process is the more commonly used method for the commercial production of lead-acid battery positive plates since the forming time is shorter than for other methods and plates of much greater electrical storage capacity can be obtained. That process involves reacting a paste usually composed of a plurality of lead oxides including for example, red lead, litharge, and the like, with dilute sulfuric acid to form a paste containing lead sulfate, basic lead sulfate and lead oxide, mechanically affixing the paste to a lead grid designed to secure the paste from removal and then electrolytically oxidizing the pasted plate to form an active material comprised mainly of lead dioxide with small amounts of lead oxide and lead sulfate. The lead sulfate is desirably present in minor quantities as required to provide a paste having the desired final bulk, and also to serve a binding function.
In U.S. Pat. No. 292,414 (1883) and U.S. Pat. No. 434,458 (1890), manganese compounds in relatively large quantities were disclosed as oxidizing agents to reduce the amount of time necessary to form the Plante electrodes and increase their capacity. In U.S. Pat. No. 566,231 (1898) and U.S. Pat. No. 911,141 (1909), manganese compounds are disclosed as binding agents for the active material. U.S. Pat. No. 1,640,922 (1927) claims an electrode paste containing 12 percent manganese peroxide to prevent discharge of the electrodes when open-circuited or dry-stored.
Chromates have also been used as oxidizing agents*, and it has been reported that ammonium chromate doubles the life of the positive active material.** On the other hand, research published in 1922*** reported that manganese caused rapid self-discharge of lead-acid batteries and severe deterioration of the positive plates. Several years later, Vinal and Altrup**** reported that manganese was particularly destructive to the positive plates. Manganese further exhibits a strong and corrosive oxidizing action on some organic materials that may be used in a battery, such as wood separators. Therefore, storage battery specifications since the 1920's typically set maximum manganese impurity levels in lead oxides for electrodes at 0.3 part***** per million (ppm) and in sulfuric acid electrolytes at 0.2 ppm. Chromium has been considered to be detrimental in storage batteries in a manner similar to manganese. FNT * George W. Vinal, "Storage Batteries", 4th Edition, (New York, 1955), pp. 23 and 132. FNT ** Morton Arendt, "Storage Batteries" (New York 1928), p. 34. FNT *** Helen C. Gillette, "A Study of Effect of Impurities on Storage Batteries", Trans. Am. Elect. Chem. Soc., XLI (1922). FNT **** G. W. Vinal and F. W. Altrup, "Effect of Certain Impurities in Storage Battery Electrolytes", Jour. Amer. Inst. Elec. Eng. (1924). FNT ***** The terms "parts" and "percent" are used herein, and in the appended claims, to refer to percent and parts by weight, unless otherwise indicated.